In conventional image forming apparatuses, various methods are employed to improve printing speed. For instance, in an image forming apparatus employing an inkjet printing method for the printing unit thereof, a black (Bk) printhead which is longer than printheads of other colors is provided to widen the range that can be printed at once, thereby improving printing speed.
Although the above conventional image forming apparatus employing an inkjet printing method can improve printing speed of a monochrome image by virtue of the long Bk printhead, there is not much improvement in printing speed of a color image. Therefore, if a monochrome image is processed as a color image by the image forming apparatus, improvement in printing speed cannot be expected.
Furthermore, in a case of performing color copying by an image forming apparatus comprising an original-document reading unit, if a monochrome image including characters or the like is processed as a color image due to a color drift which is caused at the time of reading, printing is performed with color ink instead of Bk ink, and pure monochrome printing cannot be performed.